Without limiting the scope of the invention, its background is described in connection with analytical measurements of a wide variety of analytes using a fixed optic sensor employed in sensor systems in the fields of chemical, biochemical, biological and biomedical analysis, such as a surface plasmon resonance sensor, a critical angle sensor, or a fluorescence-based sensor, for example.
Summarized briefly, a surface plasmon is known in the art as a surface charge density wave at the surface of a dielectric interface having a thin conductive film formed thereon. The oscillation of free electrons at a conductor-dielectric boundary is affected by the refractive index of the material adjacent to the film. Using a polarized beam of monochromatic light, surface plasmon polaritons can be excited. Resonance occurs when the polarized light is totally internally reflected from the conductive film. The light internally reflected from the film has a minimum intensity at the resonance angle. By detecting the resonance angle, the refractive index of a material adjacent to the film may be determined, which is indicative of other properties of the material. A more detailed description of surface plasmon resonance may be found in the article "Surface Plasma Oscillations and Their Applications," Rather, H., Physics of Thin Films, 1977.
Sensoring systems using critical angle measurements are also known in the art. Since critical angle is a mathematical function of refractive index, determination of the critical angle gives rise to the determination of the refractive index of a sample, which is indicative of one or more sample properties, from which further qualitative and quantitative analyses about the sample may be made. In a typical critical angle sensor system, when polarized light rays are directed to a sample of interest at angles of incidence smaller than the critical angle, a portion of the light is refracted into the sample, resulting in an overall loss. At angles of incidence larger than the critical angle, total internal reflection occurs, and the full intensity of the light is reflected off the sample. The critical angle, and consequently the refractive index, may be then determined by measuring the intensities of the reflected light rays, and detecting a transition from a high intensity to a low intensity. A more detailed description of critical angle sensors may be found in U.S. patent application Ser. No. 60/027,286, the contents of which are herein incorporated by reference.
The use of fluorescence based methodologies to detect sample gases and liquids is also known in the prior art. A typical application involves the molecular labeling of a film or other article followed by excitation and fluorescent measurement in the presence of the particular sample of interest. Fluorescent labeling involves the deposit of a suitable fluorescence chemistry known to interact with the sample of interest. A source of excitation light is directed at the coated article, which when brought in contact with the sample, emits a low intensity fluorescence energy. A photodetector may be used to measure the emission and therefore detect the presence of the sample. A more detailed description of fluorescence-based sensors may be found in U.S. patent application Ser. No. 60/027,287, the contents of which are herein incorporated by reference.